70 mg of 3-hydroxyazetidine monochloride, 200 mg of 1,8-diazabicyclo[5.4.0]-7-undecene, and 200 mg of pyridine were stirred at 80° C., and to this mixture was added 150 mg of 1-(3-amino-4-fluoro-6-methylphenyl)-6,7-difluoro-8-methyl-4-oxo-1,4-dihydroquinoline-3-carboxylic acid. The mixture was stirred at 90° C. for 20 minutes. Diethylether was added to the reaction solution, and the solution was decanted. 1 ml of ethanol was added to the residue and the solid precipitate was collected by filtration and dried to obtain 70 mg of the title compound.
